Optical networks are considered attractive for use in radio access networks, such as mobile front-haul networks. For example, in a mobile front-haul network, an optical network, such as a wavelength division multiplexed (WDM) optical network, may be used to couple a baseband processing unit to a plurality of remote radio units.
Separate optical fibres may be used to convey upstream and downstream optical signals respectively between the baseband processing unit and the remote radio units. However, using a single optical fibre to transmit both the upstream and downstream optical signals may save costs, which is particularly desirable in radio access networks. This is not only because fewer optical fibres may be required to transmit all of the optical signals, but also because fewer associated components such as splitters, couplers and splice enclosures may be required. Further, capital and labour costs associated with lighting up fibre may be reduced, and capital investment in fibre installations may thus be maximised. Better use may be made of existing dark fibre, and thus the “time to trench” may be extended. For example, instead of laying additional fibres, metro area networks nearing fibre exhaust, which currently use two fibres for transmission of upstream and downstream optical signals respectively, could be upgraded for single fibre operation.
In single fibre operation, in order to mitigate Rayleigh-Backscattering x-talk between the upstream and downstream optical signals, which can severely limit network performance, the upstream and downstream optical signals will typically have different wavelengths.